Flow cytometry has become an essential tool for investigators requiring high throughput analysis of single cells. Assessment of the phenotype and function of human T cells during and after a viral infection is a critical element to all CTRHIB projects (Research Projects 1-4 and Technology Development Project 1). The CTRHIB Flow Cytometry Core will provide flow cytometry services to support human immunology research by CTRHIB investigators. The Flow Cytometry Core will provide CTRHIB investigators with access to a state-of-the-art FACS ARIA flow cytometer to permit analysis and sorting of cells. Currently we are able to use 11 different flurochromes on a single sample thus allowing assessment of multiple parameters on a single cell. The core will provide training for scientists and laboratory staff to operate the FACS ARIA for data collection and analysis. It will also provide guidance in design and analysis of flow cytometry experiments, including techniques for cell staining, cell sorting and selection of antibody panels.